Sawtooth edges on 747 engines
 

I saw this on another forum and thought it might make an interesting discussion.
I have no idea what the sawtooth edges are for on these engines, but my guess would be to manage the airflow better by creating small vortices.

Since the airstream then meets the turbulent jet-wash, I'm puzzled as to how that this could be useful.

So what is the real purpose ?

Photos: Boeing 747-8R7F/SCD Aircraft Pictures | Airliners.net

Cd -

Some say it's primarily for reducing noise :

Others say it's just a Batman thing, ;) :

http://ecomodder.com/forum/attachmen...8&d=1221073641

What *is* interesting is that the design has evolved. In the pictures above, it's on the external cowling only. In this picture it is also part of a second cowling closer to the exhaust :

http://cdn-www.airliners.net/aviatio.../1/1649129.jpg

CarloSW2

...look up "scalloped fins" on whales.

Noise reduction.

Boeing: Boeing, Rolls-Royce Verify Jet Noise Reductions

The technology behind serrated trailing edge design is described in US patent 6612106 filed by Boeing in 2001.

Segmented mixing device having chevrons for exhaust noise reduction in jet engines - Patent 6612106


I wouldn't be surprised if they also reduced wake drag.

The idea is that the cold, slow surrounding air mixes smoothly with the hot, high speed jet exhaust.

In fact the jet exhaust is also the bypass air surrounding the core air, and if all these can mix with minimum turbulence that's as quiet as you can get.

Anyone old enough to remenber the lobed jetpipes of 707s - same solution to a much worse problem
illustrations and explanation here:
Noise Control/Supression
andrew

Their usage is a balance between performance (thrust) and noise (i.e. a trade off). Mixers have been around since the 60's (the sooner you get the flow mixed the quieter the engine is). What's new is the use of them on the fan cowl. The chevrons increase drag but decrease noise. Noise is a major issue these days. Ecomodders have no use for "sawtooth edges".

stealth radar dissipators?:)
andrew